Polyvinyl acetal resin is synthesized from polyvinyl alcohol as a raw material, and has an acetyl group, a hydroxy group, and an acetal group in a side chain to show excellent toughness, adhesiveness, crosslinkability, and hygroscopicity. A variation in the ratio of side chain groups can change the resin properties. Owing to such properties, polyvinyl acetal resin is used in a wide range of applications including laminated glass interlayer films for automobiles and ceramic green sheets.
An attempt is now being made to improve resin properties and develop novel functions of polyvinyl acetal resin by introducing a functional group other than the acetyl group, hydroxy group, and acetal group into a side chain of the polyvinyl acetal resin.
Polyvinyl acetal resin however has an insufficient adhesion force to metal materials. In addition, a difference in degree of shrinkage between polyvinyl acetal resin and metal materials causes warping or peeling during heat treatment for curing.
Patent Literatures 1 to 4 disclose adhesives prepared using epoxy resin. These adhesives however exert only an insufficient adhesion force to metal materials because of the insufficient strength of the resin contained.